Includes bibliographical references and index.

The challenge for educational research -- The importance of theory -- Designing research to address causal questions -- Investigator-designed randomized experiments -- Challenges in designing, implementing, and learning from randomized experiments -- Statistical power and sample size -- Experimental research when participants are clustered within intact groups -- Using natural experiments to provide "arguably exogenous" treatment variability -- Estimating causal effects using a regression-discontinuity approach -- Introducing instrumental-variables estimation -- Using IVE to recover the treatment effect in a quasi-experiment -- Dealing with bias in treatment effects estimated from nonexperimental data -- Methodological lessons from the long quest -- Substantive lessons and new questions.